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Handheld soil respiration measurements

Growing season soil CO2 fluxes are measured at respiration collars using the Li-Cor 6400 and a handheld soil respiration chamber (LiCor 6400-09).

In use at:

Collar installation

PVC collars are inserted in the soil at field sites to make soil respiration measurements with the LI-6400. Collars should be made from ~4 inch (10cm) PVC tubing to accommodate the 9.55cm diameter LiCor-6400-09 chamber. The tubing should be cut at roughly 5cm lengths and then beveled on one edge. These are inserted 1.5-3cm into the soil surface in the location where respiration is to be measured. Because installation of the collars severs roots and upsets the CO2 gradient, they should be installed at least 12 hours prior to measurement.

Measurement Procedures

Materials checklist

  • LiCor 6400 (in carrying case)
  • LiCor 6400-09 handheld soil CO2 flux chamber (attaches to the IRGA)
  • Cables/tubing for connecting items 1 and 2 (in carrying case)
  • 2 fully charged LiCor batteries
  • 2 full charged spare batteries
  • Pack frame for carrying the case (if hiking into the field)
  • Soil temperature probe (Omega Type-T thermocouple probe) assuming the LiCor 6400's is broken as usual.
  • Bring the probe AND its console
  • Notebook
  • Pen
  • Span gas tank - optional, see the notes in the measurement procedure.

Making measurements with the LI-6400

The general procedure for operating the LiCor 6400 is on the instrument page.

  • This procedure will need to be adapted for each site (see below and notes on the instrument page)

General site considerations

  • Number and location of collars
  • Depends on the site
  • Moving collars
  • Collars may remain stationary through the growing season, or they can be moved prior to each measurement.
    • This depends on research objectives.
  • Allow 12+ hours of recovery after hammering collars in at a new location.
  • Measurement frequency:
  • Every two weeks during the growing season is excellent
  • Less frequently during shoulder seasons?
  • Time of measurements:
  • Morning might be cold
  • Afternoons might be too hot
  • Night might exclude autotrophic components
  • Timing should probably be similar between measurement periods
  • Order of collar measurement:
  • If measuring a control and treatment plot, alternate the measurements so that soil temperature changes during the measurement period occur evenly between treatments.

Notes for Hidden Canyon

  • Typical Aux OP Parameters:
  • Extra drawdown = 5ppm
  • Flow = 500
  • Dead time = 20 sec
  • Minimum measurement time = 30 seconds
  • Delta of around 5-6 usually works best, more if there are lots of roots.
  • May need to modify things to stay within Target +/- Delta range.
  • Measure the soil temperature at 5cm and 15cm depths using the Omega probe (the Li-Cor one is busted)